I have had several cases where a customer has had their Active Directory-integrated DNS zones deleted, and the change replicated out to all their DNS servers before they caught the deletion. This can be a huge problem, but luckily with a system state...

Since the Vista launch, I've had several incidents with Windows 2000 Domains (be cautious with Windows 2003 too!) where a customer would join up Vista clients into their production domain and find they can't get an IP address following the reboot after...